Form a polynomial​ f(x) with real coefficients having the given degree and zeros. Degree​ 4; ​ zeros: 3​, multiplicity​ 2; 4i

Enter the polynomial. Let a represent the leading coefficient.
​f(x)=​a( )

​(Type an expression using x as the variable. Use integers or fractions for any numbers in the expression. Simplify your​ answer.)